The present invention relates to a plasma processing apparatus utilizing electron cyclotron resonance.
Recently, the ECR (electron cyclotron resonance) plasma processing method using a plasma for a film forming process or an etching process has attracted much attention. The ECR plasma processing method causes microwave discharge by using the resonance of the cyclotron motion of electrons in a magnetic field and a microwave. Since the ECR plasma processing method is able to produce a high-density plasma in a high vacuum by electrodeless discharge. the ECR plasma processing method is capable of achieving high-speed surface processing and of processing semiconductor wafers (hereinafter referred to simply as xe2x80x9cwafersxe2x80x9d) without contaminating the same.
A conventional ECR plasma processing apparatus as applied to a film forming apparatus that carries out a film forming process will be described with reference to FIG. 11. A microwave 91 of, for example, 2.45 GHz is guided into a plasma producing chamber 1A by a waveguide, not shown, and, at the same time, a magnetic field of, for example, 875 G is created by a solenoid 10 in the plasma producing chamber 1A. A plasma producing gas 92 is ionized by the agency of interaction (resonance) between the microwave and the magnetic field to produce a high-density plasma A reactive gas 93 supplied from one side of a film forming chamber 1B is activated by the plasma to produce active species. A surface of a silicon wafer W supported on a table connected to a high-frequency power source 12 is etched by sputtering and, at the same time, a film is deposited on the surface of the silicon wafer W. Thus, the ECR plasma processing apparatus carries out simultaneously processes that are opposed to each other in effect, i.e., a sputter etching process and a film forming process. The ECR plasma processing apparatus is controlled, on the whole, so that the film deposition process is dominant and a film can be deposited.
A fluorine-containing carbon film (hereinafter referred to as xe2x80x9cCF filmxe2x80x9d), which is an effective insulating film having a small relative dielectric constant, is an attractive film under circumstances where miniaturization of semiconductor devices and development of high-speed semiconductor devices are desired. The inventors of the present invention are studying a method of depositing a CF film on a surface of a wafer by an ECR plasma process using a CF gas, such as C4F8, as a reactive gas.
When a CF film is deposited on a surface of a wafer by using the conventional processing apparatus shown in FIG. 11, a portion of the CF film covering a peripheral region of the surface of the wafer is thick and a portion of the same covering a central region of the surface of the wafer is thin as shown in FIG. 12. This tendency is more remarkable with a larger wafer.
Causes of such an irregular film thickness distribution as shown in FIG. 12 have not been elucidated. The inventors of the present invention infer that such an irregular film thickness distribution is attributable to the following causes. The CF gas 93 is supplied into the film forming chamber 1B from an upper peripheral region of the film forming chamber 1B so as to flow toward a central region B corresponding to the center of the wafer as shown in FIG. 13. Consequently, the dissociation of the CF gas in the plasma progresses as the CF gas approaches the central region B corresponding to the center of the wafer and F atom (fluorine atom) concentration at a point B is greater than that at a point A in FIG. 13. F atoms produced by the dissociation of the CF gas etches a CF film deposited on the surface of the wafer. It is therefore inferred that the portion of the CF film covering the central region of the surface of the wafer is etched at a higher etch rate than the portion of the same covering the peripheral region of the surface of the wafer and, consequently, the thickness of the portion of the CF film covering the central region of the surface of the wafer is smaller than that of the portion of the CF film covering the peripheral region of the surface of the wafer.
The present invention has been made under such circumstances and it is therefore an object of the present invention to provide a plasma processing apparatus capable of uniformly processing a surface of a workpiece, such as a wafer, by using a plasma.
According to an invention stated in claim 1, a plasma processing apparatus comprising: a vacuum vessel; a stage disposed in the vacuum vessel to support a substrate thereon; a waveguide connected to the vacuum vessel from outside the vacuum vessel, the waveguide having a cylindrical outer guide member and a cylindrical inner guide member extended in the outer guide member so as to propagate a high-frequency wave through a space between the outer and the inner guide member into the vacuum vessel and so as to supply a gas through the inner guide member into the vacuum vessel from a position opposite the stage; and a high-frequency wave transmitting plate of a dielectric material disposed opposite to the stage and hermetically separating the space between the outer and the inner guide member from a space defined by the vacuum vessel; wherein a gas supplied into the vacuum vessel is ionized by the high-frequency wave propagated through the transparent plate to produce a plasma, and the substrate is processed.
According to an invention stated in claim 2, the outer and the inner guide member of the waveguide are coaxial.
According to an invention stated in claim 3, the waveguide, the inner guide member and the outer guide member are a first waveguide, a first inner guide member and a first guide member, respectively, a first waveguide is surrounded by a second waveguide having a second inner guide member surrounding the first waveguide and a second outer guide member surrounding the second inner guide member, the high-frequency wave is propagated through a space between the second inner guide member and the second outer guide member of the second waveguide, and the gas is supplied through a space between the second inner guide member of the second waveguide and the first outer guide member of the first waveguide.
According to an invention stated in claim 4, an end part of the outer guide member of the waveguide on the side of the stage is provided with a cylindrical antenna cover of a conductive material radially extending in the shape of a flange and axially extending toward the stage, and a microwave transmitting plate of a dielectric material is placed between the inside of the antenna cover and an end of the inner guide member of the waveguide on the side of the stage.
According to an invention stated in claim 5, the plasma processing apparatus further includes a magnetic field creating device capable of creating a predetermined magnetic field, wherein an ECR plasma is produced by interaction of the predetermined high-frequency wave and the predetermined magnetic field.
According to an invention stated in claim 6, the plasma processing apparatus further includes a shower head of a conductive material disposed in an end of a gas supply passage formed in the waveguide on the side of the stage and provided with a plurality of gas spraying holes opening toward the stage.
According to an invention stated in claim 7, the gas is a film forming gas containing carbon and fluorine.
According to an invention stated in claim 8, the gas is an etching gas.